Air cooled condensers have been in use in large power plants for over thirty years. Utilities worldwide now accept air-cooled condensers as an alternative to other types of cooling even if cooling water is available because the cost of cooling water has increasingly become one of the major criteria for the selection of a power plant site. By way of example, the use of an air-cooled condenser system enabled the 330 megawatt Wyodak power station erected near Gillette, Wyo., U.S.A. in 1978 to be located in an arid, coal-rich area. The power station was sited essentially on top of a seam of low sulphur coal without concern for a large plant water supply. The plant consumes only about 200 gallons per minute, mainly for boiler feed water make up.
Such a system thus easily meets or exceeds environmental regulation in terms of conservation of water while avoiding inadmissible or undesirable increases in temperature of rivers or lakes. In addition, the generation of plumes and the distribution thereof from water operated cooling towers is likewise avoided.
State-of-the-art air-cooled condensers frequently involve the so-called "A-tube" construction wherein elongated tubes of elliptical or circular cross section are arranged in an A-type configuration. Plate fins are disposed on the tube and both the tubes and the fins are typically made of steel or the like. Occasionally helically wound aluminum fins are employed as are aluminum plate fins.
The elliptical cross section provides a measure of protection against freezing of condensate within the tubes during wintery conditions, while the steel construction provides the necessary strength to allow tube lengths of 16 feet or more.
However, in order to obtain good heat transfer efficiency, it has been necessary that each branch of the A include at least two, and frequently as many as four, rows of tubes, the tubes in alternate rows generally being staggered. Needless to say, the greater the number of tube rows, the greater the air side pressure loss during operation and the greater the energy requirements for fans necessary to drive air through the air-cooled condenser. Further, multi-row constructions suffer difficulties in achieving uniform steam distribution between the rows, resulting in reduced thermal efficiency.
Another important consideration in air-cooled condensers is long life. It is necessary that the condensers have a life expectancy greater than 30, and more usually 40 years or more. Because such condensers are exposed to the ambient, it is necessary that they be highly corrosion resistant. One manufacturer promotes steel tubes with steel fins which are hot dip galvanized to avoid corrosion. This, of course, can be an extremely expensive process considering that the tanks that contain the galvanizing bath must be longer than the length of the tubes which, as noted above, frequently equal 16 feet or more. According to this manufacturer, tube and fin assemblies including a core tube helically wound with a fin or soft pure aluminum or extruded aluminum and steel assemblies, or any other type of aluminum fin are to be avoided unless they are provided with a plastic coating for corrosion resistance. This, however, eliminates action of the aluminum in producing a cathodic protective effect for the remainder of the assembly, an effect that is highly desirable when a heat exchanger may be used in any of a variety of applications where corrosion may be encountered.
Thus, notwithstanding the potential for substantial reductions both in the cost of materials used in fabricating the tube and fin assemblies, as well as erection costs of the air-cooled condensers in the field, little effort has been made to take full advantage of aluminum in tube and fin assemblies such as those that may be used in power plants and myriad other applications wherein aluminum fins are employed to achieve the higher thermal efficiencies that accompany the use of aluminum in heat exchangers due to its high thermal conductivity.
The present invention is directed to overcoming one or more of the above problems.